As is well known, naturally occurring water including surface water, ground water and conventional untreated tap water typically contains a number of salts which are dissolved out of the soil and rock. The most important constituents are the salts of sodium, calcium and magnesium. Of these, only alkaline earth metals such as calcium and magnesium are responsible for this so-called "hardness" in the water. This hardness presents problems during typical washing processes since the alkaline earth metal ions impair the washing effectiveness of the surfactants contained in conventional detergents. For this reason, builders are added to detergents so that the interaction between the metal ions and the surfactants is completely or partly avoided, thereby increasing the washing effectiveness of the surfactants. In this way, the metal ions and builders are converted to water soluble/dispersable complexes. It is preferable to avoid formation of complexes which can precipitate from the washing solution as they can deposit of the fabrics.
There have been a wide variety of builders used in detergent compositions for purposes of increasing the effectiveness of surfactants in detergents by softening, i.e. removing the hardness from washing solutions. For example, phosphate-based builders such as pentasodium triphosphate have been found to be effective in detergent formulations. The phosphate-based builders, however, have been held responsible for eutrophication of rivers and lakes, i.e. increasing the algae growth and oxygen consumption. Accordingly, measures have been taken to limit the content of phosphates in detergents.
Materials such as zeolites have been used as a substitute for phosphate builders. The zeolites are capable of the calcium ion content by ion exchange. The magnesium binding capacity, however, is very low. Thus, the use of zeolite alone in detergents has not resulted in satisfactory cleaning performance.
Further, sodium silicates have been used, as well. The chief function of these builders is to provide a supply of sodium ions and increase the pH value of the washing solutions. The use of only the amorphous version of such sodium silicates has not provided the superior cleaning now required by the industry.
Rieck, U.S. Pat. No. 4,820,439 (Hoechst), discloses the use of crystalline layered sodium silicates as detergent builders which soften water containing calcium and magnesium ions. The calcium and magnesium ion binding capacity of crystalline layered sodium silicates is indicated as being superior to amorphous sodium silicates. Rieck suggest the composition of the crystalline layered sodium silicates to have the formula NaMSi.sub.x O.sub.2x+1.yH.sub.2 O wherein M denotes sodium or hydrogen, x is from 1.9 to 4 and y is from 0 to 20. While the Rieck sodium silicates provides improved softening over amorphous sodium silicates, there is a continuing need for a combination of builders which can provide the performance required by detergent formulations.
Beerse et al, U.S. Pat. No. 5,108,646 (Procter & Gamble), disclose a process for agglomerating aluminosilicate or crystalline sodium silicate builders for use in detergent compositions. While Beerse et al provide builder agglomerates having satisfactory performance, they do not provide a detergent composition having a specific combination of builders which achieves superior cleaning performance.
Accordingly, despite the aforementioned disclosures in the art, there is a continuing need for a detergent composition having improved cleaning performance. Further, there is a need in the art for such a detergent composition which includes selected builders in an optimum ratio and achieves superior cleaning performance.